The invention relates to dynamoelectric machines and more particularly, to a dynamoelectric machine ventilation means that is operable to control the degree of intermixing between heated exhaust air leaving the machine and cooler air entering it.
Because of the direct relationship between electric motor ratings and the ability of the motors to effectively dissipate heat, many earlier inventions have been concerned with various improvements in the ventilating structures for such machines. As a consequence, the incorporation of such features as double-end ventilation, fans mounted on both ends of the rotors of electric motors, heat radiating fins mounted on the exterior housings of motors, and air flow directing baffles to afford optium circulation of cooling air around motor windings, are all well known in the prior art. For example, U.S. Pat. No. 3,725,706 - Lukens, which issued on Apr. 3, 1973 and is assigned to the same assignee as the present invention, illustrates a horizontally mountable electric motor ventilation system that incorporates one desirable form of all of these particular motor ventilation means. The application of such relatively conventional ventilating structures to either vertically mounted or horizontally mounted dynamoelectric machines is frequently merely a matter of design choice that is well within the skill of those employed in the design of both types of motors. However, the design of ventilating means for vertical electric motors poses some problems that are peculiar to such motors, and special devices must be employed to solve such problems. One basic consideration in this regard is that heated air generated by vertical motors tends to rise upward within the motor housing and along its outer surface. This flow of convection currents, coupled with other considerations unique to the design of vertical motors, makes it impractical, or in some cases impossible to utilize the type of ventilating arrangements that are suitable for cooling horizontally mounted electric motors. In general, the design of a vertical electric motor must recognize and accommodate the fact that if an identical cooling system is utilized to cool both ends of the motor there will probably be an undesirable concentration of hot spots developed at the upper end of the motor. Despite this fact, some prior art electric motors have simply utilized such horizontal-type ventilating arrangements and have accepted the consequences of operating inefficiencies resulting from the relative over-heating of the upper end turns of the motor. In other earlier vertical motor designs, exhaust air from the lower ends of the motors has been intermixed with the cooling air entering the bottom of the motors to preheat it. In such designs it is sometimes found that the bottom end of the motor actually becomes more heated than the top end.
In view of the continuing interest in increasing the operating efficiency and overall rating of electric motors, it is desirable to design vertical motors to incorporate ventilating means that provide optimum cooling efficiency for both the top and bottom end turns of the motor windings. Accordingly, it is a primary object of the present invention to provide a vertical motor ventilation means that overcomes the unbalanced cooling effect of prior art cooling systems for vertical motors.
Another object of the present invention is to provide a vertical motor ventilating means that utilizes exhaust air streams directed axially along the motor housing from both ends thereof in a manner such that the exhaust air streams form a region of turbulent intermixed air that is located substantially closer to the bottom of the motor than to its upper end.
Yet another object of the invention is to provide a vertical electric motor with a ventilating means that restricts the mixing of heated exhaust air from the motor with entering cooling air. A still further object of the invention is to provide a vertical motor with a ventilating means that incorporates uniquely formed baffles and motor end cap structures that cooperate to allow a larger stream of cooling air to enter the upper end of the motor than is allowed to enter the bottom end of the motor, and to direct streams of exhaust air from the upper end of the motor axially along its outer housing surface, while directing exhaust streams from the bottom end of the motor more radially outward from the motor housing.
Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of it given herein, considered in connection with the attached drawing.